https://learningnetwork.cisco.com/thread/6038
On Thu, Oct 28, 2010 at 5:35 PM, Garth Bryden
<hacked.the.planet.on.28.8k.dialup_at_gmail.com> wrote:
> Hiya,
>
> I have this question in my Anki Flashcards, I'm pretty sure I stole it from
> a thread where Scott Morris was assisting with the answer, so I believe its
> pretty accurate coz that guy is well freakin smart!
>
> 1. OSPF Intra Area Routes
> 2. OSPF Inter Area Routes
> 3. N1 & E1 are preferred over N2 & E2 for the same route
> 2. When N1 & E1 have the same route to the destination, The one that have
> lower cost / Metric will win and get into the route table
> 3. If both N1 & E1 have the same cost, P-bit in N1 will be used to break the
> tide.
> 4. If P-bit is 0 (Then it would become E1) then we will have 2 E1 routes
> install into the routing table. (otherwise if maximum-path = 1, LSA with
> Higher Router-ID will get installed)
>
> On Thu, Oct 28, 2010 at 2:04 PM, Maarten Vervoorn <mr.vervoorn_at_gmail.com>wrote:
>
>> Can you send me the config of R1 and R2 Only interface and ospf config.
>> Also: "show ip ospf" on r1 and r2
>> I still think R2 is the type5 type7 translator. Can you debug the ospf lsa
>> on R1 to check where it reveives those updates from
>>
>> Kind regards,
>>
>> Maarten Vervoorn
>>
>> 2010/10/28 sp-ie m <sp.ccie.me_at_gmail.com>
>>
>> > R1-R2 (12.1.1.0/24) in Area 0.
>> > R1-R3 (13.1.1.0/24) in Area 1
>> > R2-R4 (24.1.1.0/24) in Area 1
>> > R3-R4 (34.1.1.0/24)in Area1.
>> >
>> >
>> > R1-----Area0-----R2
>> > | |
>> >
>> > Area1 Area1
>> > | |
>> > R3-----Area1-----R4
>> >
>> >
>> >
>> > IP addresssing -
>> > R1 = .1
>> > R2 = .2
>> > R3 =.3
>> > R4 = .4
>> >
>> > Router IDs -
>> > R1 = 1.1.1.1
>> > R2 = 2.2.2.2
>> > R3 = 3.3.3.3
>> > R4 = 4.4..4.4
>> >
>> >
>> > Logs:
>> >
>> >
>> > R3#o d ns 134.1.1.0
>> > R3#sh ip ospf d ns 134.1.1.0
>> >
>> > OSPF Router with ID (3.3.3.3) (Process ID 1)
>> >
>> > Type-7 AS External Link States (Area 1)
>> >
>> > LS age: 111
>> > Options: (No TOS-capability, Type 7/5 translation, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 3.3.3.3
>> > LS Seq Number: 80000001
>> > Checksum: 0x2056
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 1 (Comparable directly to link state metric)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 3.3.3.3
>> > External Route Tag: 0
>> >
>> > Routing Bit Set on this LSA
>> > LS age: 116
>> > Options: (No TOS-capability, Type 7/5 translation, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 4.4.4.4
>> > LS Seq Number: 80000001
>> > Checksum: 0xB736
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 2 (Larger than any link state path)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 4.4.4.4
>> > External Route Tag: 0
>> >
>> > R3#
>> >
>> >
>> >
>> > R4#o d ns 134.1.1.0
>> > R4#sh ip ospf d ns 134.1.1.0
>> >
>> > OSPF Router with ID (4.4.4.4) (Process ID 1)
>> >
>> > Type-7 AS External Link States (Area 1)
>> >
>> > Routing Bit Set on this LSA
>> > LS age: 60
>> > Options: (No TOS-capability, Type 7/5 translation, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 3.3.3.3
>> > LS Seq Number: 80000001
>> > Checksum: 0x2056
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 1 (Comparable directly to link state metric)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 3.3.3.3
>> > External Route Tag: 0
>> >
>> > LS age: 65
>> > Options: (No TOS-capability, Type 7/5 translation, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 4.4.4.4
>> > LS Seq Number: 80000001
>> > Checksum: 0xB736
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 2 (Larger than any link state path)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 4.4.4.4
>> > External Route Tag: 0
>> >
>> > R4#
>> >
>> >
>> > R1#sir 134.1.1.0 l
>> > Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
>> > D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
>> > N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
>> > E1 - OSPF external type 1, E2 - OSPF external type 2
>> > i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
>> > ia - IS-IS inter area, * - candidate default, U - per-user static route
>> > o - ODR, P - periodic downloaded static route
>> >
>> > Gateway of last resort is not set
>> >
>> > 134.1.0.0/24 is subnetted, 1 subnets
>> > O E1 134.1.1.0 [110/85] via 13.1.1.3, 00:02:02, Serial1/1
>> >
>> > R1#o d ns 134.1.1.0
>> > R1#sh ip ospf d ns 134.1.1.0
>> >
>> > OSPF Router with ID (1.1.1.1) (Process ID 1)
>> >
>> > Type-7 AS External Link States (Area 1)
>> >
>> > LS age: 466
>> > Options: (No TOS-capability, Type 7/5 translation, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 3.3.3.3
>> > LS Seq Number: 80000001
>> > Checksum: 0x2056
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 1 (Comparable directly to link state metric)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 3.3.3.3
>> > External Route Tag: 0
>> >
>> > LS age: 471
>> > Options: (No TOS-capability, Type 7/5 translation, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 4.4.4.4
>> > LS Seq Number: 80000001
>> > Checksum: 0xB736
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 2 (Larger than any link state path)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 4.4.4.4
>> > External Route Tag: 0
>> >
>> > R1#o d ex 134.1.1.0
>> > R1#sh ip ospf d ex 134.1.1.0
>> >
>> > OSPF Router with ID (1.1.1.1) (Process ID 1)
>> >
>> > Type-5 AS External Link States
>> >
>> > Routing Bit Set on this LSA
>> > LS age: 447
>> > Options: (No TOS-capability, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 2.2.2.2
>> > LS Seq Number: 80000001
>> > Checksum: 0xEA0F
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 1 (Comparable directly to link state metric)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 3.3.3.3
>> > External Route Tag: 0
>> >
>> > R1#
>> >
>> >
>> >
>> > R2#sir 134.1.1.0 l
>> > Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
>> > D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
>> > N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
>> > E1 - OSPF external type 1, E2 - OSPF external type 2
>> > i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
>> > ia - IS-IS inter area, * - candidate default, U - per-user static route
>> > o - ODR, P - periodic downloaded static route
>> >
>> > Gateway of last resort is not set
>> >
>> > 134.1.0.0/24 is subnetted, 1 subnets
>> > O N1 134.1.1.0 [110/149] via 24.1.1.4, 00:06:47, Serial1/1
>> > R2#
>> > R2#o d ex 134.1.1.0
>> > R2#sh ip ospf d ex 134.1.1.0
>> >
>> > OSPF Router with ID (2.2.2.2) (Process ID 1)
>> >
>> > Type-5 AS External Link States
>> >
>> > LS age: 493
>> > Options: (No TOS-capability, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 2.2.2.2
>> > LS Seq Number: 80000001
>> > Checksum: 0xEA0F
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 1 (Comparable directly to link state metric)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 3.3.3.3
>> > External Route Tag: 0
>> >
>> > R2#sh ip ospf d ns 134.1.1.0
>> >
>> > OSPF Router with ID (2.2.2.2) (Process ID 1)
>> >
>> > Type-7 AS External Link States (Area 1)
>> >
>> > Routing Bit Set on this LSA
>> > LS age: 522
>> > Options: (No TOS-capability, Type 7/5 translation, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 3.3.3.3
>> > LS Seq Number: 80000001
>> > Checksum: 0x2056
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 1 (Comparable directly to link state metric)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 3.3.3.3
>> > External Route Tag: 0
>> >
>> > LS age: 527
>> > Options: (No TOS-capability, Type 7/5 translation, DC)
>> > LS Type: AS External Link
>> > Link State ID: 134.1.1.0 (External Network Number )
>> > Advertising Router: 4.4.4.4
>> > LS Seq Number: 80000001
>> > Checksum: 0xB736
>> > Length: 36
>> > Network Mask: /24
>> > Metric Type: 2 (Larger than any link state path)
>> > TOS: 0
>> > Metric: 20
>> > Forward Address: 4.4.4.4
>> > External Route Tag: 0
>> >
>> >
>> >
>> > On Wed, Oct 27, 2010 at 6:50 PM, sp-ie m <sp.ccie.me_at_gmail.com> wrote:
>> > > Hey guys,
>> > >
>> > > I'm confused if Intra-area N1 will be left out and Inter-Area E1 will
>> > > be chosen if E1 is seen from highest router-id NSSA ABR .
>> > >
>> > > I hv a square topology.
>> > >
>> > > Area 1 is NSSA.
>> > >
>> > > R1-----Area0-----R2
>> > > | |
>> > > Area1 Area1
>> > > | |
>> > > R3-----Area1-----R4
>> > >
>> > > R1-R2 in Area 0.
>> > > R1-R3 in Area 1
>> > > R2-R4 in Area 1
>> > > R3-R4 in Area1.
>> > >
>> > > Router ID R1 = 1.1.1.1
>> > > R2 = 2.2.2.2
>> > > R3 = 3.3.3.3
>> > > R4 = 4.4..4.4
>> > >
>> > > Question: Both R3 and R4 are redistributing a static route 134.1.1.0
>> > > into Area1. R3 is redistributing it as N1 while R4 as N2.
>> > > On R2, I can see it receives 134.1.1.0/24 as N1 from R4. This makes
>> > > perfect sense as N1 is pref over N2.
>> > >
>> > > On R1, I can see it receives 134.1.1.0/24 as E1 route from R2 but the
>> > > next hop is R3's interface IP. This part is tricky.
>> > > Which rule says that E1 from Inter-area neighbor will supersede N1
>> > > from local area?? I know this is somehow happening coz R4 has highest
>> > > router-ID NSSA ABR but dont quite understand how intra-area N1 is left
>> > > out and Inter-Area E1 is chosen.
>> > >
>> > > Tried a cursory look in few popular workbooks but didnt find similar
>> > issue.
>> >
>> >
>> > Blogs and organic groups at http://www.ccie.net
>> >
>> > _______________________________________________________________________
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>>
>>
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>>
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>
>
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>
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Received on Thu Oct 28 2010 - 23:58:13 ART
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